FAQ
Last Updated 2000-03-28
What is Metadata?
What is the purpose of Dublin Core metadata?
Why is it called the "Dublin Core"?
 What
is "Simple Dublin Core"?
What
is "Qualified Dublin Core"?
Who uses Dublin Core?
Is Dublin Core metadata intended to be used only
for digital (electronic) resources?
What
is the Warwick Framework?
How can I store Dublin Core Metadata?
How can I store Dublin Core Metadata in HTML?
What is the relationship between Dublin Core Metadata
and RDF and XML?
What is the Dublin Core datamodel?
Can
I add a new element to Dublin Core?
How
do I store names in Dublin Core?
What is the maximum length for each field in
Dublin Core?
Please explain the one to one (1:1) rule.
What search-engines support Dublin Core?
How do I participate in discussion about Dublin
Core?
Workshops?
What is the relationship between Dublin Core
and other Internet standards groups?
Is there metadata on the Dublin Core Metadata
Initiative's web site pages?
What is Metadata?
The simplest useful definition of metadata is "structured
data about data." This very general definition includes
an almost limitless spectrum of possibilities ranging from human-generated
textual description of a resource to machine-generated data
that may be useful only to software applications..
The term metadata has been used only in the past 15
years, and has become particularly common with the popularity
of the World Wide Web. But the underlying concepts have been
in use for as long as collections of information have been organized.
Library catalogs represent a well established variety of metadata
that has served for decades as collection management and resource
discovery tools.
What is the purpose of Dublin Core metadata?
Dublin Core metadata is specifically intended to support resource
discovery. The elements represent a broad, interdisciplinary
consensus about the core set of elements that are likely to
be widely useful to support resource discovery.
Why is it called the "Dublin Core"?
The original workshop was
held in Dublin, Ohio, hence the term "Dublin Core."
The DC directorate is located in Dublin, Ohio at the Online
Computer Library Center, a nonprofit organization that serves
the networking needs of libraries in the US and some 70 other
countries. The Dublin Core Metadata Initiative itself, however,
is very much international in scope.
What is Simple Dublin Core?
"Simple Dublin Core" is a term often used to describe
Dublin Core metadata that uses no qualifiers (see "Qualified
Dublin Core" below). That is, the elements are expressed
as attribute-value pairs using just the 15 elements from the
Dublin Core Metadata
Element Set without any further information about encoding
schemes, enumerated lists of values, or other processing clues.
The term "unqualified Dublin Core" is synonymous
with "simple Dublin Core."
What is Qualified Dublin Core?
"Qualified Dublin Core" is a term applied to Dublin
Core metadata that employs additional information to increase
the specificity of the metadata by refining the meaning , by
specifying encoding schemes or controlled vocabularies, or to
indicate a metadata value is a compound, or structured value.
For example, a date may be further identified as a particular
variety of date (date last modified, date published, etc.) and
might be encoded according to a particular scheme that assures
that it can be interpreted unambiguously. A subject term that
is the value of the Subject element might be specified as having
been selected from a particular controlled vocabulary such as
the Dewey Decimal Classification.
Qualifiers allow applications to increase the specificity or
precision of the metadata, but also introduces complexity that
can impair interoperability. Thus, designers of metadata systems
are well advised to be conservative about deploying qualifiers
in cases where interoperability is one of the design objectives.
Dublin Core interoperability qualifiers are those which have
been approved in the Dublin Core community and are a formal
part of the registry of Dublin Core metadata. Designers should
select qualifiers that come from this set to the extent that
they meet the functional requirements for a given application.
It is expected that local or application-specific requirements
may well require additional qualifiers, or even additional elements,
that have not been approved by the Dublin Core community at
large. Deployment of local qualifiers and extensions is an appropriate
action, but designers should do so with the understanding that
interoperability with other applications may suffer. In cases
where such additional qualifiers are being deployed, it may
be helpful to bring this to the attention of the Dublin
Core Directorate in order to promote the wider use of such
qualifiers.
Who uses Dublin Core?
Anyone can use Dublin core elements as a convenient basis for
descriptive systems. Web pages are one of the most common types
of resources to have Dublin Core descriptions, often using
HTML meta tags. But bulk conversions of descriptive information
stored in older catalog systems and databases probably made
up the largest number of Dublin Core descriptions in the early
days of the initiative. Dublin Core metadata is being used as
the basis for descriptive systems by several specialised communities
and agencies: community based
interest groups currently exist for education, libraries,
government, and research. Also see the listing of Dublin
Core based projects.
Is Dublin Core metadata intended to be used
only for digital (electronic) resources?
The Dublin Core Metadata Initiative began in 1995
to develop conventions for resource discovery on the World Wide
Web. The focus of discussion was electronic resources. It was
clear at the outset, however, that the semantics of resource
discovery should be independent of the medium of the resource,
and that there are obvious advantages for using the same semantic
model across media. Thus, considerable attention has been invested
in making the Dublin Core sufficiently flexible to represent
resources (and relationships among resources) that are both
digital and exist in traditional formats as well.
What is the Warwick Framework?
The Warwick Framework is a conceptual model for metadata that recognizes that
different packages of metadata, about the same thing, might be useful for different
purposes and created, according to different standards or by different agencies.
These will coexist, and mechanisms for generating and storing metadata should
make allowances for this requirement. XML namespaces are one example of a tool
which underpins the Warwick Framework approach.
The Warwick Framework is not a system, but rather a set of
design principles that have helped guide the development of
the Dublin Core since the Second Dublin Core Metadata Workshop
in Warwick, UK. Please read "The
Warwick Metadata Workshop: A Framework for the Deployment of
Resource Description" for more information.
How can I store Dublin Core Metadata?
The Dublin Core Metadata Element Set is a set of semantic definitions
of 15 descriptive elements. This means that many different methods
can be used to actually record or transfer Dublin Core metadata.
Common methods include HTML, XML, RDF and relational databases.
Nevertheless, there are various limitations associated with
the different methods that should be taken into account if planning
a system.
For example, HTML is convenient since it keeps
the metadata embedded together with a document content, but
only supports a simple list of meta elements, with no grouping
or other structure.
XML allows much more structured data to be recorded, and mechanisms
such as XML namespaces can add value. However, there are few
software applications available to use XML encoded data yet,
and those that exist require considerable configuration or programming.
RDF, which was developed partly by people
from the Dublin Core community, probably has the greatest expressive
potential, but software to support RDF is currently experimental.
For best performance in searching and retrieval, it is probably
best to load DC metadata into a database management system,
but this then forces the detachment of the metadata from the
resource which it describes, so system designers must be careful
to implement procedures to ensure consistency and synchronisation.
How can I store Dublin Core Metadata in HTML?
Dublin Core metadata can be stored using the meta
element in the head of HTML documents. An information
"RFC" issued by the IETF Encoding
Dublin Core Metadata in HTML defines the standard way to
do this. A Note issued
by DCMI describes one method for storing Qualified DC in HTML.
What is the relationship between Dublin Core
Metadata and RDF and XML?
Dublin Core Metadata is about semantics... what we are trying
to say about resources.
RDF is about structure...
the conventions for encoding the assertions about a resource
that uses Dublin Core Metadata semantics.
XML provides the
syntax for encoding assertions in RDF, and hence in RDF-encoded
Dublin Core Metadata.
Dublin Core Metadata and RDF are distinct specifications. Neither
requires the other, but their co-evolution make them natural
complements in the metadata architecture for the Web. The Dublin
Core community and the RDF community have a number of members
in common, and they have evolved together. The Dublin Core community,
in fact, provided many (but not all) of the basic requirements
that were used to design RDF. In turn, the development of RDF
provided the Dublin Core community with a much more formal underlying
data model which has helped the DC community find principled
solutions (rather than ad hoc Band-Aids) for many of the detailed
problems that arise in deployment.
What is the Dublin Core datamodel?
A datamodel is an abstract representation of the part of the
world that a system is designed to service. It typically includes
its scope - i.e. an indication of the range of objects
of interest to the system; the properties of things which
are in-scope, and some kind of specification of interactions
between them.
The RDF datamodel is quite simple
- "things have properties", where each property
has a name and a value. The "atom" of RDF, therefore,
has three components: the thing (resource, in web terminology),
a property name, and a property value.
- each resource may have several of these properties.
- the value may itself be a resource.
Dublin Core builds on RDF by:
- defining 15 named properties - the Dublin Core Metadata
Element Set - which are considered to be widely useful for
resource discovery.
- specifying that a resource may have any number, including
zero, of each of these properties (elements, in DC
terminology).
- defining the range of resource types that may have DC descriptions
- given by the allowed values for the DCMES Type element.
which defines the basic Dublin Core datamodel.
Several of the 15 DC elements record relationships between
the resource-of-interest and another resource which is in-scope
for DC. In particular, Relation and source are used to indicate
a connection with another resource of any type. Creator, Contributor
and Publisher relate the present resource to a party
who has some responsibility for it. Coverage relates the present
resource to a place or to a time-period. The Value recorded
for each of these elements, therefore, should normally be strictly
an identifier of another resource, which could, in principle,
have its own DCMES description. In this way, it is possible
that a web of DC descriptions of resources will be constructed,
with each resource at the centre of a fan of descriptive
arcs, but connected via one of these relationships to other
resources with their own fans. Of course, the "identifiers"
will, in many cases, use an informal notation in plain-text.
However, many users have found it useful to add extra information
to Dublin Core descriptions, in particular:
- values are frequently drawn from a controlled vocabulary
(e.g. a keyword list, such as Library of Congress Subject
Headings, LCSH), or written using a special notation (e.g.
the ISO8601 format for dates and times), or use a particular
natural language (in the case of values written in text-strings),
so it would make the information more useful if a client were
informed of the source of this vocabulary, the definition
of the notation, or the name of the language used.
- an instance of an element may be used in a specialised way,
with more restricted semantics than implied by the broad definition
of the element (e.g. the Date might be the date a resource
was modified)
To encompass these requirements, the qualified Dublin
Core datamodel also includes:
- value qualifiers - to store an identifier for the vocabulary,
encoding or language of the value.
- element qualifiers - to refine the meaning of the element.
A DCMES element qualified with an element qualifier is, effectively,
a "new" element or property, with a more specialised
meaning than its parent element.
Note, however, that it is not possible to create a new Dublin
Core element with a meaning that goes beyond the meaning of
the meaning of elements in the DCMES. To extend a description
beyond that supported by DCMES, other mechanisms must be used.
Can I add a new element to Dublin Core?
As its name implies, the Dublin Core is a starting place, not
a final word. It is expected that local applications will add
elements to meet local or community needs. Local extensions
should be clearly distinguished from the Dublin Core through
the use of a notational mechanism, such as using a prefix or
namespace. Elements which are part of a local extension will
not normally be useful to others that they have not been subject
to the cross-community consensus building process that has brought
the Dublin Core element set to its current state. Implementors
are, however, encouraged to bring such elements to the attention
of the community so that others might adopt them as judged necessary,
leading possibly to eventual approval as additional Dublin Core
elements.
The Australian
Government Locator Service is an example of a major implementation
of Dublin Core metadata which has added four local elements
to Dublin Core in the recommended way.
How do I store names in Dublin Core?
The encoding of personal names is fraught with many difficulties
in Dublin Core metadata, as in other types of metadata systems.
Conventions differ from culture to culture. The recommendation
for Dublin Core metadata is to encode family name first, which
supports effective collation of names and is consistent with
most naming conventions globally. Two Notes have been written
about the difficulties of personal names among cultures. One
was written by Diane Hillmann (Names
in Dublin Core) and the other by Andrew Waugh (Representing
People's names in Dublin Core).
What is the maximum length for each field
in Dublin Core?
There are no limits to field length.
Please explain the one to one (1:1) rule.
The 1:1 rule expresses the notion that a discrete resource should have a discrete
metadata record. Seems simple enough. Unfortunately, it isn't always so neat because
resources are often not so discrete (Should each photograph in an article have
its own record? What about collections of articles? Can the collection be thought
of as a resource? What about multimedia objects?)
Some in the Dublin Core community now believe that the 1:1
principle should be revisited, and a working group will address
these issues and recommend guidelines to promote consistent
application.
If you are interested in joining this group (dc-one2one), either
as an active participant or as a listener, please visit the
Dublin Core working group area on the Mailbase Server (http://www.mailbase.ac.uk).
The site provides directions for joining (and leaving) mailing
groups. Names of all Dublin Core mailing lists begin with dc-
and can be found under D in the list of groups.
Which search-engines support Dublin Core?
Several commercial and noncommercial search-engines will index
meta elements with just a little configuration.
A recent inquiry on the dc-general mailing list produced this
list:
To get a good overview of what software is out there see Search
Tools and Search
Engine Watch.
The famous "all the web" search engines like AltaVista,
Yahoo, HotBot, etc. tend to avoid using the information found
in meta elements in their indexing. This is because,
unless the pages are from guaranteed "trusted" servers,
the meta information is commonly used by unscrupulous
content-providers for spamming, to mislead the indexes into
giving web-pages a misleading rating.
How do I participate in discussion about
Dublin Core?
You can sign up for any of the DC mailing lists or working
groups at the Mailbase server. Go to: http://www.mailbase.ac.uk
and follow the instructions for joining a mailing list. The
names of all Dublin Core mailing lists start with dc- (click
on Discussion Lists and then on D).
Workshops?
Information will be posted on the Dublin Core Homepage (http://purl.org/dc)
on how to nominate yourself for upcoming workshops. Please note that workshops
are not introductory workshops, but are intended for those who are implementing
Dublin Core and are interested and able to contribute time and effort in advancing
the state of the art.
What is the relationship between Dublin
Core and other Internet standards groups?
The Dublin Core Metadata Initiative (DCMI) is a consensus building
organization that has relationships in many standards activities.
A number of people in the DCMI are active in the W3C
(DC is the prototype application that drove the development
of the Resource Description Framework, or RDF in the W3C). Our
own standardization activities take place in the IETF
(RFC
2413 is reference description of the initial version of
the Dublin Core), and there are currently formal DC standardization
activities underway in CEN
(the European information industry standardization forum) and
in NISO (the North American
information standardization organization).
Is there metadata on the Dublin Core Metadata
Initiative's web site pages?
All of the DC pages have metadata associated with them. For
practical management purposes, we've associated external metadata
linked by the HTML LINK element.
When you view source on http://purl.org/dc/index.htm
you'll find
<LINK REL="meta" HREF = "index.htm.rdf"
/>, take a look at http://purl.org/dc/index.htm.rdf
and you'll find what you're looking for.
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